A successor communication scheme to W-CDMA (Wideband-Code Division Multiple Access), HSDPA (High Speed Downlink Packet Access), HSUPA (High Speed Uplink Packet Access) and other schemes, that is, a LTE (Long Term Evolution) scheme, are being discussed in W-CDMA standardization group 3GPP. As radio access schemes for the LTE, OFDM (Orthogonal Frequency Division Multiplexing) and SC-FDMA (Single Carrier-Frequency Division Multiple Access) schemes are promising for downlinks and uplinks, respectively. For example, see 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA”, June 2006.
The OFDM scheme is a multi-carrier transmission scheme where a frequency band is segmented into multiple smaller frequency bands (subcarriers) and data is transmitted in the individual subcarriers. The subcarriers are orthogonally and densely arranged on a frequency axis, which can achieve faster transmission and improve frequency utilization efficiency.
The SC-FDMA scheme is a single-carrier transmission scheme where a frequency band is segmented for different terminals and the divided frequency bands are used by the different terminals for transmissions. According to the SC-FDMA scheme, not only can interference between the terminals be easily and effectively reduced but also variations of transmit power can be suppressed. As a result, the SC-FDMA scheme is preferred from some standpoints such as reduced power consumption for terminals and wider coverage.
In the LTE system, for both uplinks and downlinks, one or more resource blocks are assigned for a user apparatus or a user equipment terminal (which is typically a mobile station but may be a fixed station) for communications. The resource blocks are shared among a large number of mobile stations in the system. In the LTE system, a base station apparatus determines for which of the multiple mobile stations the resource blocks are assigned for each subframe having 1 ms. This process is referred to as scheduling. The subframe may be referred to as a transmission time interval (TTI). In the downlinks, the base station apparatus transmits a shared channel in one or more resource blocks to a mobile station selected in the scheduling. In the uplinks, the selected mobile station transmits a shared channel in one or more resource blocks to the base station apparatus.
Meanwhile, user apparatuses transmit random access channels (RACHs) to base station apparatuses at initial accessing such as power activation time, at requesting of resource assignment, and at resynchronization such as at handover failure time. The base station apparatuses receive the RACHs and transmit information necessary for subsequent communications to the user apparatuses. It is expected that the RACHs may be used in the LTE system and other mobile communication systems. In the LTE system and other mobile communication systems, variable system bandwidths may be used, for example, 1.4 MHz, 5 MHz, 10 MHz and 20 MHz. For example, 3GPP TS 25.214 discloses a conventional technique for periodically providing timings when the RACHS may be transmitted at initial activation time. The system bandwidth disclosed in this reference is not variable, unlike the LTE system, and the RACHs are transmitted in the overall frequency band. Also, it is desirable that the RACHs be orthogonally multiplexed with other signals from the standpoint such as improved signal quality. For this point, the LTE system may differ from conventional systems where a CDM (Code Division Multiplexing) scheme is presumed. At the present time, it may not be fully studied when the RACHs are to be transmitted in the systems using variable system bandwidths such as the LTE system. See 3GPP R1-070103, “Downlink L1/L2 Control Signaling Channel Structure: Coding” for reference.